1. Field of the Invention
The present invention relates to optical systems and, in particular, to an optical packaging design for optical filters, isolators and the like.
2. Technical Background
There is considerable interest in the field of optics, particularly relating to the area of telecommunication systems. Optical fibers are the transmission medium of choice for handling the large volume of voice, video, and data signals that are communicated over both long distances and local networks. Much of the interest in this area has been spurred by the significant increase in communications traffic which is due, at least in part, to the Internet. Important components of fiber optic networks are the optical filters concatenated into the wavelength division multiplexing (WDM) modules, optical isolators, and similar devices which modify, shape, and block light signals. These devices may be subjected to various thermal and mechanical stresses/during assembly, production, environmental testing, and operations. It is critical to the operation of the network that these devices function reliably over their projected 20 to 25 year service life. Further, these devices represent a significant portion of the cost of a network. Therefore, it is desirable to reduce the cost of these important components.
An example of a typical filter device is illustrated schematically in FIG. 1. The device functions as follows. A light signal 11a travels through optical fiber 12a which is positioned in a capillary of input glass ferrule 13a. The signal 11a exits the fiber 12a and travels through input collimating lens 14a where the signal is collimated into parallel rays and directed to thin film filter 15b which is deposited on a glass substrate 15a. Filter 15b modifies the light signal 11 as the signal travels through filter 15b. The signal 11 then travels through the output collimating GRIN lens 14b where the signal is directed to the output fiber 12b. 
The typical filter package is further illustrated in the cross-section view of FIG. 2. In addition to the components shown in FIG. 1, there is shown the insulating glass sleeves 21a and 21b, metal sleeves 22a and 22b, outer metal enclosure 23, and solder or weld joints 24a and 24b. 
While these packages can function well, there are two areas which must be continually improved upon. These are cost and reliability. These devices continue to be expensive due to the numerous parts required and the high cost of some components. As can be seen in the figures, the device has multiple identical components. For example, there are two ferrules 13a and 13b, two collimating GRIN lenses 14a and 14b, two insulating glass sleeves 21a and 21b, two metal sleeves 22a and 22b, and two solder or weld joints 24. All of these components are not only costly, but they also result in time and labor costs to assemble these precision devices. Further, an increased number of components generally reduces yield while increasing the failure rate. Of particular concern are the solder or weld joints 24 which create a hermetic or near hermetic seal for the device. If either one of these joints 24 fail, it increases the chance of a device failure. Also, the most significant cost of the device is the filter element itself. A single filter may cost several hundred dollars. A device, system, or method to reduce the costs and improve reliability would be a significant advantage.
Finally, any package design should be adequate not only to mechanically protect the fragile optical components but also to compensate for and minimize the thermally induced shift in spectral performance.
The continuing goal, therefore, is to find ways to reduce costs and improve quality and reliability of optical filtering packages. It is also a goal to design a package that is simple in construction and miniaturized.